This invention generally relates to electrophotographic and electrographic imaging processes, and more specifically, the present invention is directed to improved imaging processes wherein electrophoretic liquid developer compositions are applied from an applicator roll in a manner that enables only the charged areas of the image bearing member to be developed, thereby minimizing ink vehicle carryout. Therefore, in one embodiment of the present invention there is provided an electrostatic lithography process wherein electrostatic latent images are developed with electrophoretic liquid developer compositions comprised of a nonvolatile insulating fluid, charged pigment particles, and a stabilizer component; and wherein the aforementioned composition is applied to an imaging member by an applicator roll, such as a gravure roll whereby there is enabled ink wetting of only the charged areas of the imaging member.
Electrophotographic and electrographic imaging processes with liquid developers are generally known. There is described, for example, in U.S. Pat. No. 3,954,640 liquid developer compositions which dry at ambient temperatures by penetration into paper, and wherein there remains a continuous film having excellent rub resistance on the surface thereof, which inks contain, for example, pigment and/or dye, resinous particles dispersed in a liquid carrier, dispersing agent, and from about 25 to about 90 percent by weight of a nonvolatile high boiling organic liquid carrier and/or solvent. More specifically, the types of inks utilized in the process of the '640 patent are illustrated in column 3, beginning at line 50, and continuing on to column 4. As noted in column 4, beginning at line 30, examples of hydrocarbon oils or mineral oils which may be selected include Magie Oil 520 and 620 having boiling points of within the range of 270 to 296.degree. C., and 293 to 362.degree. C., respectively. A similar teaching is presented in U.S. Pat. No. 4,024,292.
Illustrated in U.S. Pat. No. 3,084,043, the disclosure of which is totally incorporated herein by reference, is a liquid development process wherein there is selected, for example, a gravure roller; and wherein water based inks or oil based inks can be selected, reference column 2, lines 7 through 25. Inks selected for the process of the '043 patent are illustrated in column 7, beginning at line 42, and include those containing a water or oil soluble dye dissolved in water or oil; and there may also be selected alcohol base inks with additives therein such as ethylene glycol, see column 7, beginning at line 50. One disadvantage associated with the aforementioned inks and the processes thereof reside in the formulation of images of decreased resolution and with substantial background deposits in some situations, which disadvantages are alleviated with the processes of the present invention wherein there is selected, for example, oil based ink compositions with the characteristics indicated.
Other patents with similar teachings and directed to liquid developers include U.S. Pat. Nos. 3,806,354; 4,268,597; 3,669,886 and 3,901,696.
Additionally, there is illustrated in U.S. Pat. No. 3,806,354 the disclosure of which is totally incorporated herein by reference, liquid inks comprised of one or more liquid vehicles, colorants such as pigments, and dyes, dispersants, and viscosity control additives. Examples of vehicles disclosed in the aforementioned patent are mineral oils, mineral spirits, and kerosene; while examples of colorants include carbon black, oil red, and oil blue. Dispersants described in this patent include materials such as an alkylated polyvinyl pyrrolidone. Also, there are described in U.S. Pat. No. 4,476,210, the disclosure of which is totally incorporated herein by reference, liquid developers containing an insulating liquid dispersion medium with marking particles therein, which particles are comprised of a thermoplastic resin core substantially insoluble in the dispersion, an amphipathic block or graft copolymeric stabilizer irreversibly chemically, or physically anchored to the thermoplastic resin core, and a colored dye imbibed in the thermoplastic resin core. The history and evolution of liquid developers is provided in the '210 patent, reference columns 1 and 2 thereof.
Although the above described liquid inks and processes are suitable in most instances for their intended purposes, there remains a need for new processes, particularly wherein electrophoretic liquid developer compositions are selected. More specifically, there is a need for imaging processes wherein undesirable ink vehicle carryout is minimized or substantially eliminated. In addition, there is a need for imaging processes wherein an electrophoretic ink is applid from an applicator such as a gravure roller configured in a manner that the liquid is electrostatically attracted to only the charged areas of the image bearing surface. Moreover, there is a need for liquid development processes wherein the ink composition contains an insulating fluid, particularly a nonvolatile component, thus permitting absorption of these components into paper substrates and eliminating environmental hazards, particularly insulating fluid evaporation into the surrounding atmosphere. Furthermore, there is a need for electrostatic processes wherein electrophoretic inks whose dielectric relaxation time is less than the process time are obtainable. Additionally, there is a need for a liquid development process wherein the ink residue remaining on the photoreceptor surface subsequent to image transfer and cleaning will not cause degradation of subsequent images due to electrical conduction over the surface of the photoconductor. There is also a need for imaging processes with electrophoretic particles present in the ink, which particles have attached thereto long chain polymers to prevent flocculation of the ink particles, yet permit their adhesion to paper. Also, there remains a need for liquid development processes wherein electrophoretic inks are applied from gravure applicators, and wherein the inks are caused to move in synchronism with the electrostatic image present on a conductive imaging member thereby enabling high development speeds and also limiting contact of the ink composition with charged regions of the imaging member, thus substantially eliminating undesirable solvent carryout. In addition, there is a need for imaging processes with ink compositions of certain characteristics, which compositions can be easily cleaned from the photoreceptor surface, have extended shelf life, and which are free of environmental hazards. These and other needs are obtainable with the process of the present invention.